False positives, or false counts, are undesirable in any inspection situation. False counts in an inspection system can arise from multiple sources. This may include electronic noise associated with detectors in the system as well as external noise associated with photons or radiative particles from sources other than the sample of interest. In the context of inspection systems, a false count occurs when a signal not associated with a sample is detected by one or more detectors and is incorrectly associated with properties of the sample. Radiation sources that may affect the false count rate of an inspection system may include, but are not limited to, the decay of trace levels of radioactive isotopes near the inspection system as well as high energy cosmic radiation by-products generated in the atmosphere. These radiation sources may produce radiative particles and/or photons including, but not limited to, alpha particles, beta particles, neutrons, muons, and gamma rays. For example, muons are primarily generated as a by-product of the interaction of cosmic radiation with the atmosphere. Radiative particles can also be generated through inelastic scattering from materials in close proximity to the inspection system.
Advances in the application of multi-pixel detectors in inspection systems have resulted in increased conversion gain and lower noise readout electronics. However, these advances have also resulted in increased sensitivity to the detection of particle radiation, such as muons, gamma particles, and alpha particles, to name a few. Therefore, it is desirable to provide a method and system that cures the defects identified above in previous approaches.